In recent years, a liquid crystal display device in which the height and width of a display screen are interchangeable is developed. In a case where in such a liquid crystal display device, a backlight unit that uses a fluorescent lamp as a light source is incorporated, the display screen is changed in the height and width, so that disadvantages arise as described below.
Usually, a fluorescent lamp (e.g., cold-cathode tube) has electrodes (filaments) on both ends of a tube; rare gases such as mercury, argon and the like are confined in the inside of the tube; moreover, a fluorescent-body film is disposed on an inner surface of the tube. And, such a fluorescent lamp makes electrons emitted via the electrode collide with mercury atoms present in the discharge tube. And, ultraviolet rays generated by the collision excite the fluorescent body coated on the inner surface of the tube to generate and emit visible light to outside of the tube.
And, to emit such light, mercury must exist between both electrodes in the fluorescent lamp. However, in a case where the fluorescent lamp is situated along a gravity direction, mercury collects on one electrode, while no mercury exists on the other electrode. Because of this, if both electrodes are discharged in the fluorescent lamp in such a state, electrons do not collide with mercury atoms, so that mercury (ineffective mercury) that is not vaporized remains in the fluorescent lamp. If the ineffective mercury exists in the fluorescent lamp during light emission, the brightness of the fluorescent lamp becomes low and the electrodes deteriorate.
Accordingly, to prevent such disadvantages, in a liquid crystal display device in a patent document 1, a U-shape fluorescent lamp is incorporated. And, even if the display screen is changed in the height and width, the liquid crystal display device does not orient a tip end of the U-shape fluorescent lamp downward in a gravity direction. Because of this, the mercury does not collect on one electrode that is situated at the tip end (U-shape tip end) of the fluorescent lamp to surely exist between both electrodes. As a result of this, the ineffective mercury does not appear in the fluorescent lamp during light emission, so that the disadvantages due to the ineffective mercury are eliminated.